In digital communications networks it is generally necessary that the sending end of the network and the receiving end of the network be synchronized in order to recover the transmitted information.
Synchronization techniques are known for time division multiplexed (TDM) digital transmission systems. Some such techniques have been proposed. See, for example, U.S. Pat. No. 4,316,284, which is entitled "Frame Resynchronization Circuit for Digital Receiver" and which issued to R. D. Howson on Feb. 16, 1982, as well as U.S. Pat. No. 4,316,285, which is entitled "Frame Circuit for Digital Receiver" and which issued to R. T. Bobilin et al. on Feb. 16, 1982.
It is known that, in time division multiplexing (TDM) systems, digital information is transmitted in frames and synchronization is realized by properly locating the frames by a process called framing in which the sending end and the receiving end recognize the same frame boundaries, i.e. recognize the same first bit of a frame through the same last bit of the frame.
In the cited U.S. Pat. No. 4,316,284, for example, bits of a received time division signal are compared with bits of a code word generated in accordance with a prescribed criterion from the received time division signal to, thereupon, generate code word error indications. The reframing process is iterated until the receiver is synchronized on a framing bit pattern for which there is no code word error indication generated. That is, the received signal is monitored to determine whether code word bits inserted in the time division signal match code word bits that are locally generated in the receiver from the received time division signal. The U.S. Pat. No. 4,316,284 discloses, in one example, the use of a six bit cyclic redundancy check (CRC) code word. The CRC code word is employed with the code word bits being inserted in predetermined ones of the framing bit positions of the time division signal.
In packet communications networks, it is known to employ an error check sequence in an attempt to maintain end-to-end integrity of transported packets. It is possible that the error check sequence can be used in a manner disclosed in the U.S. Pat. Nos. 4,316,284 and 4,316,285 to realize synchronization.
Notwithstanding, in the process of framing, as the bit or group of bits is slipped, the code word is generated over the whole frame or other predetermined portion of the received signal, which involves time and, hence, needs additional speed improvement. Accordingly, it remains desirable to improve synchronization methodology in a communications network to mitigate such problems.